It is increasingly common for motor vehicles to have monitoring systems for safety purposes, these systems having sensors mounted on each of the wheels of the vehicle, used for measuring parameters, such as pressure or temperature, of the tires fitted on these wheels, with the aim of informing the driver of any abnormal variation in the measured parameter.
These monitoring systems conventionally have an electronic module mounted on each wheel of the vehicle, incorporating, in addition to the aforesaid sensors, a microprocessor and a radio frequency transmitter, while the system also has a central unit for receiving the signals sent by the transmitters, including a computer incorporating a radio frequency receiver connected to an antenna.
One of the problems to be resolved by these monitoring systems lies in the requirement for each signal received by the receiver of the central unit to be associated with a data element relating to the location of the electronic module, and consequently the location of the wheel from which this signal originated, this requirement continuing throughout the life of the vehicle; that is to say, it must be met even after wheel changes or, more simply, after reversals of the wheel positions.
Numerous methods are currently proposed for achieving this location of the position of the wheels of a vehicle, including location methods such as those described, notably, in patents EP 0 806 306 and EP 0 895 879, the principle of which is based on the correlation present between the signals delivered by a sensor fitted to a wheel and the signals delivered by a sensor mounted on the vehicle in the proximity of this wheel.
Since most present-day vehicles are fitted with active safety systems such as the ABS anti-lock system for wheels and the ESP system for dynamic stability control, these location methods are, notably, of considerable value in terms of installation cost, since the wheel location is performed by correlating the signals delivered by the sensors of said active safety system with the signals delivered by the sensors normally integrated into the electronic modules of the monitoring system.
Consequently, the application of these location methods simply requires the implementation of software for processing the delivered signals, without the need for additional special hardware.
At present, however, these location methods are restricted to electronic modules mounted on the rims of vehicle wheels.
This is because the problem of signal transmission for fixed angular positions of the electronic modules is fully resolved when the sensors are integrated into electronic modules mounted on the rims of the wheels. On the other hand, the measurement environment is completely different when the electronic module is fixed to the inner face of the tread of a tire: on each revolution, this electronic module comes into contact with the ground and is therefore subjected to an impact which causes the invalidation of the strategy for determining the angular position of said electronic module.